1. Field of the Invention
The invention relates to an electromagnetic solenoid which is connected to an oil hydraulic control valve to actuate it. More particularly, it is directed to an improvement of the solenoid which facilitates flow of oil loaded into the solenoid from the hydraulic control valve by movement of a movable core of the solenoid.
2. Related Art
FIG. 7 is a longitudinal sectional view showing a conventional electromagnetic solenoid for oil hydraulic control valves, the upper half of which shows a post-operation state and the lower half of which shows a pre-operation state. FIG. 8 is a side view of the electromagnetic solenoid shown in FIG. 7. In FIGS. 7 and 8, an electromagnetic coil 1 is wound around a bobbin 2, and a lead wire 3 of the electromagnetic coil 1 passes through and extends out from a grommet 16. A case 4, which is made of a magnetic metal, contains the electromagnetic coil portion 1. One end of the case 4 has an oil flow hole 4a extending in its axial direction, and a male screw portion 4b is provided at its outside diameter portion. A magnetic path iron core 5, which is made of a magnetic metal and firmly coupled with the case 4 while caulked by a flange 5a. Reference numeral 6 designates a fixed iron core. An operating rod 7, which is made of a nonmagnetic material, is movable in its axial direction, and its rear end is supported by the magnetic path iron core 5 through a slide roll bearing 8, while its front end is supported by the case 4 through a sleeve bearing 9. A movable iron core 10 is secured to the operating rod 7. The outer surface on the rear end side of the movable iron core 10 corresponds with the inside diameter of the magnetic path iron core 5 and its front end confronts with the rear end of the fixed iron core 6. Reference numeral 11 designates a buffer spring for receiving the withdrawing operating rod 7; 12, a nonmagnetic spring receptacle; 13, 14, O rings; 15, a filler resin body used to fill a gap formed between the inner surface of the case 4 and the electromagnetic coil 1.
The electromagnetic solenoid thus constructed is screwed into a housing 17 of the oil hydraulic control valve at the male screw portion 4b of the case 4 and an end of the operating rod 7 is in contact with a valve rod 18 of the hydraulic control valve. Reference numeral 19 designates an O ring.
The operation of such an electromagnetic solenoid will be described next. Normally, the electromagnetic coil 1 is not energized. Thus, the operating rod 7 is set to a withdrawal position while resisting the spring pressure of the buffer spring 11 by return of the valve rod 18 caused by a return spring (not shown) of the oil hydraulic control valve.
When the electromagnetic coil 1 has been energized, the movable iron core 10 is attracted toward the fixed iron core 6, causing the operating rod 7 to advance in the direction of A while moving the valve rod 18 ahead.
In the meantime, operating oil within the housing 17 of the oil hydraulic control valve is filled in the case 4 through the oil flow hole 4a. To allow a smooth flow of oil, the following means are provided.
(1) The oil flow hole 4a of the case 4; PA0 (2) A gap between the inside diameter of the fixed iron core 6 and the outside diameter of the operating rod 7; PA0 (3) A gap 20 between the movable iron core 10 and the fixed iron core 6; and PA0 (4) A gap between the inside diameter of the magnetic path iron core 5 and the outside diameter of the movable iron core 10.
However, the conventional electromagnetic solenoid thus constructed has entailed the following problems.
(1) The oil flow hole 4a must be provided at the front end portion of the case 4, which requires cumbersome work of drilling a small-diameter, long hole.
(2) An oil flow path must be provided by a gap 20 between the front end of the movable iron core 10 and the rear end of the fixed iron core 6 with the operating rod 7 being at the advance position, and this has required a stopper portion 21 to be provided at the inner end of the inside diameter portion on the front end side of the case 4 so that advance of the operating rod 7 can be stopped.
(3) A gap between the inside diameter of the magnetic path iron core 5 and the outside diameter of the movable iron core 10 serves as an oil flow path, and this increases the air gap of the magnetic path, resulting in reduced magnetic property and impaired response.